INVESTIGATIONS OF GROUND-BASED CLOUDS AT THE MT-BROCKEN

Results of the 1996 field season (April-November) of the cloud chemist ry program starting in 1992 at the Mt. Brocken are presented. The moun tain site (1142 m a.s.l.) is located in the Hart Mountains/Germany. Fo r a large part of the database (about 40%), both cloud water and drizz le and/or precipitation were present at the same time. A separation in to two groups was done: non-precipitating clouds and mixed category of events. More than 2000 one hour samples were collected and analysed f or major ions. The mean cloud water pH for the frostfree period in 199 6 was 3.9. Histograms giving the distribution of pH values show that t he pH values of samples from non-precipitating clouds ranges from 2.5 up to values > 8 and that the distribution is bimodale. For the 1996 f ield season period as a whole, pH values of cloud water were lower tha n those of mixed samples (cloud water, drizzle, precipitation) at the Brocken site. This was related to higher concentrations of all ions in cloud water. Cloud base measurements using a ceilometer confirmed the correlation between liquid water content and height above cloud base and consequently the influence of sampling height relative to the clou d base on the total ionic content of cloud water.